Various types of laser plotters are known in the art. There are two general types: flat bed plotters and drum plotters.
Both types are well known, and are produced and marketed by several companies including the present application/assignee.
Plotters of the internal drum variety have been proposed but technical problems requiring complex optomechanical solutions have made such plotters a relatively expensive product. An example of one such internal drum plotter is described in Computer Technology Review, Summer, 1984, pages 199-203 and in a catalog sheet issued by the manufacturer, Macdonald Dettwiler and Associates Ltd., of Richmond, British Colombia, Canada. This device, identified as FIRE 9000 is stated to include a single faceted air bearing spinner and precision linear micropositioner for ensuring high line quality and geometric accuracy.
Penta prisms, which are known to be insensitive to wobbling in directions perpendicular to the axis of rotation thereof, have been used in flat bed scanners, as shown in U.S. Pat. No. 4,475,787 to Starkweather, but have not been proposed for use in internal drum scanners. In the Starkweather patent, which is particularly suited for flat bed plotters, the penta prism is arranged in association with a lens in the path of the output light beam from the penta prism for focusing the parallel planes of the light beam into a fine point of light defining a scan line. While Starkweather deals adequately with the problem of wobble, it greatly reduces the effective duty cycle of the apparatus, thus significantly slowing its operation.